When Apple refused to help the FBI break into an iPhone which was used by one of the San Bernadino shooters the government agency sought help from elsewhere. Eventually they ended up working with hackers to overcome the security of the handset in order to find new leads to pursue in the wake of the event. And it turns out the job was not cheap.

FBI Director James Comey had this to say about how much the hack cost:

"A lot. More than I will make in the remainder of this job, which is seven years and four months for sure, But it was, in my view, worth it"

CNBC went digging into official salary records for the FBI and found that Comey's current annual salary is $183,300 so added up over his remaining time in the post that comes to a total of $1.34 million for the job. That sum makes it the highest ever public fee for hacking, and an idea of the kind of security it takes to successfully get into someone's phone and also strike a deal with the FBI which won't see you go to jail.

And it turns out the technology can be used again, with the FBI now able to access iPhone 5C handsets running iOS 9. It's pretty clear the debate over smartphone security is going to continue for a long while yet.